Depth sounders are used by watercraft to echo-locate underwater terrain and to locate and identify fish. They do this by sending out a burst of acoustic energy from a transducer, and then subsequently use the same transducer to receive the returned echoes, and amplify and display the echoes on a CRT or LCD display. Conventional depth sounders, as implemented in small and medium sized boats, send out the energy collimated in a single beam, and by repeatedly pinging the transducer, use the motion of the boat to "paint" a two dimensional image of the area over which the boat has passed. More elaborate systems, that move the transducer beam either mechanically or electronically, are too large and too expensive for the small boat owner.
However, it is desired by the small to medium sized boat owner to have a depth sounder that can paint an image of the region under a boat, without using boat motion to provide one axis, and do this in real time or near real time. This could be done with a phased array, which electrically deflects the beam, if the size and cost were within practical limits for the small boat owner.
A phased array is an array of transducers, usually arranged in a linear row, the individual transducers being individually excited with a sinusoidal voltage that has an appropriate delay and/or phase shift to produce a beam of energy in a pre-determined angle or direction. For a linear array, the possible angles of beam deflection are limited to the plane formed by a line through the array elements and a line normal to the transmitting surfaces of the array. See FIG. 1. Techniques of this type date back many years using both acoustic and electromagnetic energy. An early patent using only delay line techniques for submarine echo-location is described in U.S. Pat. No. 3,037,185 by G. H. DeWitz. Later patents using delay lines combined with frequency conversion and summation, describe a means of phase control for dynamic focusing, as in U.S. Pat. Nos. 4,140,022 and 4,699,009 by S. Maslak. The principle technique described in these later patents is the use of a combination of delay lines and mixer phasing to control the deflection angle and focal point of the beam.